SE2230352A1 - Pulp mill - Google Patents

Abstract

A pulp mill comprising a screening arrangement (2) for screening pulp, a reject handling arrangement (3a-b) connected to the screening arrangement to receive a reject therefrom, the reject handling arrangement being arranged to convey at least portion of the reject to storage means for disposal thereof, and a washing arrangement (4) connected to the screening arrangement, the washing arrangement being configured to wash at least a portion of an accept received from the screening arrangement. The reject handling arrangement, the screening arrangement and the washing arrangement are arranged consecutively within an elongated area portion of the pulp mill, such as on an elongated platform. An overhead or gantry crane (6a-c) arrangement is displaceable along a lengthwise direction of platform, the crane arrangement being configured to co-act with the screening arrangement, the washing arrangement and the reject handling arrangement.

Description

TECHNICAL FIELD The invention relates to the field of pulp mills for producing cellulose pulp, for example using the Kraft process.

BACKGROUND Pulp mills for carrying out processes such as the Kraft process and sulfite process are well known in the art. Pulp mills comprise a plurality of devices such as reactors, towers and washing devices to be able to carry out the process. The relative placement of the devices varies depending on the customer's needs, but in general, the devices are arranged in accordance with the process flow and form a pulp mill having an elongated footprint, typically with the cooking arrangement (digester etc.) at a first short end of the pulp mill, and pulp storage towers for the end-product (bleached/delignified cellulose pulp) at a second (opposite) end of the pulp mill. The reject handling is typically placed at a side (long end) of the pulp mill to allow convenient removal of the portion of the reject which cannot be recirculated to the digester.

At certain locations, the above-described type of conventional pulp mill layout is disadvantageous due to limited land space and/ or high land prices. Further, maintenance work may be complicated in such a conventional pulp mill layout.

SUMMARY An object of the invention is to provide a pulp mill which is improved in terms of allowing simplified maintenance and/or in terms of having a more compact layout, i.e. having a smaller footprint.

These and other objects are achieved by the present invention by means of a pulp mill according to the independent claim.

According to a first aspect ofthe invention, there is provided a pulp mill comprising a screening arrangement for screening pulp cooked from wood chips, a reject handling arrangement connected to the screening arrangement to receive a reject therefrom, the reject handling arrangement being arranged to convey at least portion of the reject to storage means for disposal thereof, and a washing arrangement comprising at least one washing device connected to the screening arrangement, the at least one washing device being configured to wash at least a portion of an accept received from the screening arrangement. The reject handling arrangement, the screening arrangement and the washing arrangement are arranged consecutively within an elongated area portion of the pulp mill, such as on an elongated platform. Optionally, the pulp mill comprises a cooking arrangement, which is arranged to receive wood chips and to subject the wood chips to a cooking process to produce pulp, wherein the screening arrangement is arranged to receive pulp from the cooking arrangement.

In other words, the reject handling arrangement, the screening arrangement and the washing arrangement are arranged consecutively, i.e. after one another along a line (which preferably is substantially straight) within an area portion of the pulp mill which is substantially longer than wide (since the arrangements are arranged consecutively). The area portion may be defined by an elongated (raised) platform on which the reject handling arrangement, the screening arrangement and the washing arrangement are arranged. Such arrangements are advantageously arranged on a platform since this allows one or more material flows therefrom to be conveyed by means of gravity. The area portion or elongated platform may extend substantially from one short end of the pulp mill to its opposite short end. The optional cooking arrangement may be arranged to subject the wood chips to a kraft cooking process to produce the pulp.

The invention may alternatively be described in that the reject handling arrangement, the screening arrangement and the washing arrangement are arranged consecutively along a line (which may be substantially straight) extending in the direct from one short end of the pulp mill to the other.

It is understood that an arrangement being arranged at or adjacent a side or long end of the elongated area / platform does not necessarily imply that the arrangement is in abutment or direct contact with the area/platform but may also comprise embodiments where one or more additional devices are disposed between the area/platform and the arrangement. It is furthermore understood that the washing arrangement may comprise additional washing devices, for instance washing devices connected to delignification reactors and/or bleaching towers for washing the output therefrom. The washing arrangement may, but does not necessarily, comprise all washing devices of the pulp mill.

The inventors have realized that by arranging not only the screening and washing arrangements consecutively, but also the reject handling arrangement, for instance on an elongated platform, access to the arrangements may be improved such that maintenance is simplified. Furthermore, simplified piping may be achieved.

In embodiments, the pulp mill further comprises an overhead or gantry crane arrangement being displaceable along a lengthwise direction of area or platform, the crane arrangement being configured to co-act with the screening arrangement, the washing arrangement and the reject handling arrangement. Such embodiments are advantageous since the same crane arrangement can be used for maintenance or other work on all three arrangements. The overhead crane arrangement may comprise a bridge comprising one or more beams which is travelling (for example using wheels, sliding means or the like) along an overhead fixed runway/rail structure extending along the lengthwise direction of the elongated area or platform, and where one or more trollies or sliding devices, such as two trollies/sliding devices, is/ are displaceable along the bridge in a substantially perpendicular direction to the runway/rail structure. One or more, or each of the trollies/sliding devices may comprise or support a hoisting mechanism. The runway/rail structure may for example be connected to the long end walls of a building structure enclosing the elongated area or platform. The gantry crane arrangement may correspond to the above-described overhead crane arrangement except that the bridge is supported by legs to form a substantially U-shaped element which travels on a (non-overhead) fixed runway/rail structure extending along the lengthwise direction of the elongated area or platform, for instance at a base of the area or platform.

In embodiments, the cooking arrangement is disposed at/adjacent a first long side of the area/platform, i.e. the cooking arrangement is arranged at one side (long end) of the area/ platform, i.e. to the side of one or more of the reject handling arrangement, the screening arrangement and the washing arrangement. The cooking arrangement is thus arranged at a long end/side of the pulp mill to the side of one or more of the reject handling arrangement, the screening arrangement and the washing arrangement. This embodiment is advantageous since placing the cooking arrangement at a side/ long end of the elongated platform facilitates access to the short end of the platform, for instance for removal of waste from the reject handling arrangement.

In embodiments, the reject handling arrangement is disposed at a short end of said elongated area or platform such that said storage means is accessible from said short end. The storage means may for example comprises containers or other types of vessels. In embodiments where the reject handling arrangement is disposed on an elongated (raised) platform, the storage means is arranged below (wholly or at least partly beneath) the platform to allow easy access for vehicles and to allow conveying the reject to the storage means by gravity.

In embodiments, the pulp mill further comprises one or more electrical feeding arrangements connected to at least one of the cooking, screening, reject handling and washing arrangements to provide electrical power thereto, wherein at least one of the electrical feeding arrangements is disposed at a second long side of the platform, the second long side being opposite the first long side.

In embodiments, the pulp mill further comprises pulp storage means being arranged to receive washed pulp directly or indirectly from the washing arrangement, said pulp storage means being disposed at a first long side of the platform. The pulp storage means may comprise storage towers which may have a height to diameter ratio being greater than 2,5:1.

In embodiments, the pulp mill further comprises a delignification arrangement and / or a bleaching arrangement being arranged at/adjacent said first long side. The washing arrangement may further comprise at least one additional washing device, each being arranged to co-act with the delignification arrangement and/ or a bleaching arrangement, for instance in the sense that the additional washing device is arranged to receive delignified or bleached pulp from a delignification or bleaching reactor. The delignification arrangement and/ or a bleaching arrangement may comprise one or more devices (such as reactors) having a height to diameter ratio being greater than 2,5:1.

In embodiments, the cooking arrangement comprises an impregnation tower, a digester and a blow tank. At least one, or each, of the impregnation tower, digester and blow tank may have a height to diameter ratio being greater than 2,5:1.

In embodiments, the reject handling arrangement is furthermore arranged to convey at least part of the reject to feeding means for recirculation back to said digester or blow tank. The reject may be recirculated to the digester in the form of a suspension. Such recirculation and the devices (pumps etc.) are well known in the art and will not be described in further detail here.

In embodiments, the screening arrangement comprises at least one coarse screening device and at least one fine screening device. The screening arrangement may furthermore or alternatively comprise a combined coarse and fine screening device. Such screening devices are well-known in the art and will not be described in further detail here.

In embodiments, each constituent part of the pulp mill having a height to diameter ratio greater than 2,5: 1 is disposed at said first long side of the platform. This may be advantageous since piping is simplified and since maintenance may be more convenient.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features.

BRIEF DESCRIPTION OF THE DRAWINGS Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show a presently preferred embodiment of the invention, wherein fig. 1 shows a schematic top view of an embodiment of the pulp mill according to the invention, and fig. 2 shows a schematic side view of parts (the platform, a washing device and the gantry crane) ofthe embodiment in fig. 1.

DETAILED DESCRIPTION Fig. 1 shows a schematic top (2D) view of an embodiment of the pulp mill according to the invention.

The pulp mill comprises a cooking arrangement 1 arranged to subject the wood chips to a Kraft pulping process. The cooking arrangement comprises an impregnation tower 1a arranged to receive wood chips and to impregnate the wood chips with cooking liquor, a pressurized digester 1b and a blow tank 1c to which the finished cooked wood chips are blown. The pulp mill furthermore comprises a screening arrangement 2, a reject handling arrangement 3a-b and a washing arrangement 4 which are all arranged consecutively on an elongated platform 5. The cooking arrangement 1 is disposed at a first long side 5b of the platform.

The pulp from the blow tank is fed to the screening arrangement 2 which comprises a fine screening device and a coarse screening device. The reject from the screening arrangement is fed to the reject handling arrangement 3a-b, the reject handling arrangement being arranged to convey at least portion of the reject to storage means in the form of containers 3c-d for disposal thereof. The reject handling arrangement is disposed at a short end 5a of the elongated area or platform such that the storage containers are accessible from the short end. The containers 3c-d are arranged below the platform 5. The reject handling arrangement 3a-b is arranged to convey at least part of the reject to feeding means, which may be considered part of the reject handling arrangement, for recirculation back to the Cooking arrangement (impregnation tower or blow tank).

The washing arrangement 4 comprises two serially arranged washing devices 4a being twin-roll presses connected to the screening arrangement 2 configured to wash at least a portion of an accept from the screening arrangement 2 in two stages.

The washed pulp from the washing devices 4a is fed to a delignification arrangement 9 comprising a first oxygen delignification reactor 9a, a second oxygen delignification reactor 9b which is connected to a blow tank 9c and a medium consistency (MC) tower 9d. The delignification arrangement co-acts with washing devices 4b (also twin-roll presses) of washing arrangement 4. For example, one or two washing devices is / are connected between the blow tank 9c and the MC tower 9d, and a washing device is arranged after the MC tower 9d.

The delignified pulp is fed from the MC tower of the delignification arrangement 9 to the bleaching arrangement 10. The bleaching arrangement comprises three serially arranged bleaching towers (DO, EOP, D1 as seen from the right to the left). The bleaching arrangement co-acts with washing devices 4c (also twin-roll presses) of washing arrangement 4, a first washing device being connected between the DO and EOP bleaching towers, a second washing device between the EOP and D1 bleaching towers, and the third between D1 bleaching tower and the pulp storage towers 8a, 8b. In other embodiments, the DO bleaching stage may be replaced with a Dht stage, and/or the EOP bleaching stage may be replaced with a EO or EP stage.

The delignification arrangement 9, the bleaching arrangement 10 and the pulp storage towers 8a- b are all arranged at the first long side 5b of the platform 5.

An electrical feeding arrangement 7a is connected to the screening, reject handling and washing arrangements to provide electrical power thereto. The electrical feeding arrangement 7a is arranged at a second long side 5c of the platform, the second long side being opposite the first long side 5b.

The pulp mill further comprises a gantry crane arrangement being displaceable along a lengthwise direction of platform 5, the crane arrangement being configured to co-act with the screening arrangement, the washing arrangement and the reject handling arrangement. The gantry crane arrangement comprises a bridge 6a formed by two parallel beams, which bridge is supported/elevated at its ends by legs 6c to form a substantially U-shaped element which travels on a fixed runway/rail structure 6d-e extending along both long ends 5b-c, i.e. in the lengthwise direction of the elongated platform. Two trollies 6b, 6b' each supporting a hoisting mechanism is displaceable along the bridge in a substantially perpendicular direction to the runway/rail structure 6d-e.

Each part ofthe pulp mill having a height to diameter ratio greater than 2,5:1 is arranged at the first long side 5b of the platform. The pulp mill further comprises liquor buffer tanks 12a, 12b and filtrate tanks 11a-e. The tank 12b has a height to diameter ratio greater than 2,5:1, which means that it is arranged at the first long side 5b, whereas the tanks 11a-e and 12a each has a height to diameter ratio smaller than 2,5:1, which means that they are all arranged at the second long side 5c.

The pulp mill optionally comprises an additional electrical feeding arrangement 7b for feeding the adjacent cooking arrangement 1, and a heat exchanging arrangement 13 (also co-acting with the cooking arrangement).

Fig. 2 shows a schematic side view of parts of the embodiment in fig. 1 (as seen from the left in fig. 1). In fig. 2, the platform 5 is seen, which is raised above the ground level by means of being supported by leg portions 5a, 5b. One of the washing devices 4c (a twin-roll press) of washing arrangement 4 is schematically shown arranged on the platform 5. In fig. 2, the above-described gantry crane arrangement is shown in more detail. The gantry crane arrangement comprises a bridge 6a formed by two parallel beams (only one is seen in the side view in fig. 2), which bridge is supported/elevated at its ends by legs 6c, 6c', wherein wheels 6f, 6f are provided at the lower ends ofthe legs 6c, 6c' such as to travel on a fixed runway/rail structure 6d, 6e. Two trollies 6b, 6b' each supporting a hoisting mechanism are displaceable along the bridge in a lateral direction (substantially perpendicular to the runway/rail structure 6d-e). Consequently, the trollies/hoisting mechanisms are displaceable both in the lengthwise and lateral direction ofthe platform and can co-act with the screening arrangement, the washing arrangement, and the reject handling arrangement, for example to conduct maintenance work thereon. For example, the hoisting mechanism can be used to engage with and lift a roll/drum from the twin-roll press 4c for repair or replacement.

All of the above-described devices, such as impregnators, digesters, blow tanks, twin-roll presses, screening devices, delignification reactors, bleaching towers, heat exchangers are well-known in the art and will not be described in further detail here. Pipes, conduits or the like interconnecting the devices and arrangements as described above are considered to be self-evident for the persons skilled in the art and are thus not shown in the figures.

The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the gantry crane may be substituted with an overhead crane or omitted altogether. Furthermore, the number and type of washing devices, delignification reactors, bleaching towers, pulp storage towers, filtrate tanks and so on may be varied. Furthermore, although fig. 1 illustrates a Kraft pulp mill having a specific configuration, other processes and Kraft processes deviating from the illustrated are also contemplated within the scope of the claims.

Claims (7)

1. A pulp mill for producing cellulose pulp comprising: - A screening arrangement (2) for screening pulp; - A reject handling arrangement (3a-b) connected to the screening arrangement (2) to receive a reject therefrom, the reject handling arrangement being arranged to convey at least portion of the reject to storage means (3c-d) for disposal thereof; - A washing arrangement (4) comprising at least one washing device (4a) connected to the screening arrangement (2), the at least one washing device being configured to wash at least a portion of an accept received from the screening arrangement, wherein the reject handling arrangement (3a-b), the screening arrangement (2) and the washing arrangement (4) are arranged consecutively on an elongated platform (5), further comprising an overhead or gantry crane arrangement (6a-c) being displaceable along a lengthwise direction of platform, the crane arrangement being configured to co- act with the screening arrangement, the washing arrangement and the reject handling arrangement.

2. Pulp mill according to claim 1, wherein said crane arrangement comprises a bridge (6a) comprising one or more beams displaceable along a fixed runway or rail structure extending along the lengthwise direction of the elongated platform, and one or more trollies or sliding devices (6b, 6b') being displaceable along the bridge in a substantially perpendicular direction to the lengthwise direction.

3. Pulp mill according to claim 2, wherein one or more, or each of the trollies or sliding devices (6b, 6b') comprises or supports a hoisting mechanism.

4. Pulp mill according to any of the preceding claims, further comprising a cooking arrangement (1) arranged to receive wood chips and to subject the wood chips to a cooking process, wherein the screening arrangement is arranged to receive pulp from the cooking arrangement.

5. Pulp mill according to claim 4, wherein said cooking arrangement is disposed at a first long side (5b) ofthe platform.

6. Pulp mill according to any of the preceding claims, wherein the reject handling arrangement (3a-b) is arranged at a short end (5a) of said elongated platform (5) such that said storage means (3c-d) is accessible from said short end.

7. Pulp mill according to any of the preceding claims, further comprising an electrical feeding arrangement (7a) connected to at least one of the screening, reject handling and washing arrangements (1, 2, 3a-b) to provide electrical power thereto, the electrical feeding arrangement being arranged at a second long side (5c) of the platform, the second long side being opposite the first long side (5b). Pulp mill according to any of the preceding claims, further comprising pulp storage means (8a-b) arranged to store cellulose pulp produced at the pulp mill, said pulp storage means being disposed at a first long side (5b) of the platform. Pulp mill according to claim 7 or 8, further comprising a delignification arrangement (9) and/ or a bleaching arrangement (10), said delignification arrangement and/ or bleaching arrangement being arranged at said first long side (5b). Pulp mill according to claim 9, wherein said washing arrangement (4) further comprises at least one washing device (4b, 4c) arranged to co-act with one or more reactor of the delignification arrangement and / or a bleaching arrangement. Pulp mill according to any of the preceding claims, wherein each constituent part of the pulp mill having a height to diameter ratio greater than 2,5:1 is disposed at said first long side (5b) of the platform. Pulp mill according to claim 4 or any of claims 5-11 as dependent on claim 4, wherein said cooking arrangement (1) comprises an impregnation tower (1a), a digester (1b) and a blow tank (1c). Pulp mill according to claim 12, wherein said reject handling arrangement (3a-b) is furthermore arranged to convey at least part of the reject to feeding means for recirculation back to said digester or blow tank. Pulp mill according to any of the preceding claims, wherein said screening arrangement (2) comprises at least one coarse screening device and at least one fine screening device. Pulp mill according to any of the preceding claims, wherein said cooking arrangement (1) is arranged to subject the wood chips to a kraft cooking process.